This application relates to an apparatus and method for electrochemical detection of an analyte in a sample. The invention utilizes a specific binding relationship between the analyte and at least one reagent provided in the apparatus as a means for detecting the analyte.
Analysis methods in which specific binding between an analyte and a reagent forms the basis for the assay are known. For example, in enzyme-linked immunoassay (EIA or ELISA) procedures, a sandwich is formed between an immobilized antibody and a mobile enzyme-antibody reagent when analyte is present through the interaction of the analyte with the antibody components. This results in the immobilization of the enzyme. The subsequent detection of immobilized enzyme is therefore indicative the presence of analyte in a test solution. (See U.S. Pat. Nos. 3,654,090, 4,169,012, and 4,642,285) Similar sandwich assays are used in chromatographic immunoassays where a colored tag (for example a colored latex bead) on the mobile reagent becomes trapped on a substrate at a defined location to produce a pattern that indicates the presence of analyte in a sample. (See U.S. Pat. Nos. 4,943,522, 5,656,503, 5,712,172 and 5,766,961) Analysis methods that depend on specific binding between an analyte and a reagent may also take the form of competition assays, in which the formation of a complex involving a labeled reagent is inhibited in the presence of analyte in an analyte-concentration dependent manner (See U.S. Pat. Nos. 4,868,131, 5,981,298 and 5,989,921), or displacement assays in which a pre-existing complex involving a labeled reagent is disrupted in the presence of analyte in an analyte-concentration dependent manner. (See U.S. Pat. Nos. 4,746,631 and 6,020,209).
Immunoassays in which detection of the analyte depends on an electrochemical measurement are also known. U.S. Pat. No. 5,149,630 discloses an assay in which the extent to which the transfer of electrons between an enzyme substrate and an electrode, associated with the substrate reaction, is perturbed by complex formation or by displacement of any ligand complex relative to unbound enzyme-labelled component. This determination is made in the presence of an applied potential. An applied potential is also used to measure current in the assay device disclosed in U.S. Pat. Nos. 5,198,367, 5,427,912. U.S. Pat. No. 5,494,831 discloses the application of a current and the measurement of changes in impedance that result in binding.